Carcinomas are the most common form of cancer, and are responsible for the majority of cancer-related deaths worldwide. Early detection of cancer improves a prognosis significantly, as evidenced by the 70% reduction in mortality in cervical cancer after the Papanicolaou test became accepted as a routine annual examination in the United States. Likewise, mortality rates from breast cancer have been reduced by up to 30% because of earlier detection through manual examination and mammograms. Unfortunately, the relative inaccessibility of most body tissues currently limits the breadth of cancer screening. Even when tumors are detected by existing techniques and removed surgically, there is a strong inverse correlation between tumor size and out-come, such that cancer survival rates are higher when tumors are detected early and removed while the tumors are relatively small in size.
The analysis of accessible body fluids for the detection of neoplastic cells should greatly facilitate earlier cancer detection, and the detection of micro-metastases in body fluids of patients who have early stage cancer could have a substantial impact on optimizing therapeutic regimens and, thus, long-term prognosis. Unfortunately, even when cancer is present in a patient, the relative number of cancer cells in readily accessible bodily fluids such as blood is generally quite small, making cancer detection by sampling bodily fluids very challenging. Classic microscopy-based analysis, although the gold standard in diagnostics, lacks the throughput required to identify rare cell populations consistently and with confidence. Flow cytometry offers much higher data acquisition rates, but flow cytometery depends largely on the availability of fluorescently labeled markers to discriminate between normal cells and neoplastic cells, and tumor-specific markers generally have not yet been identified.
The use of an antibody-based approach to address this problem depends on ectopic expression of a normal antigenic epitope, formation of a new epitope through genetic mutation or recombination, or consistent modulation of the expression of a marker expressed in transformed and non-transformed cells. The approach is confounded further by the diversity of neoplastic transformations and genetic heterogeneity in the human population.
In contrast to single- or multi-parameter antibody-based techniques, cellular morphology analysis is an effective means of cancer screening. For instance, dysplastic and neoplastic cells are detected in lung sputum on the basis of morphology. Likewise, exfoliated cells collected from bladder washings of bladder cancer patients are shown to have distinct morphologic and genetic changes. Dysplastic morphology is also the primary diagnostic criterion in Papanicolaou smears, where microscope-based auto-mated morphologic analysis is shown to be effective and approved by the Food and Drug Administration for primary screening.
Studies have indicated that cancer cells exhibit morphological characteristics that can be used to differentiate cancer cells from normal cells, however, most instruments capable of acquiring cellular images having enough detail to enable such morphological characteristics to be discerned do not have the throughput required to be able to detect very small numbers of cancer cells hidden in relatively large populations of normal cells. This problem is significant, because studies have indicated that the blood of a majority of patients who have had metastatic carcinomas contains fewer than one detectable carcinoma cell per 7.5 mL of blood, which is below the current threshold of five circulating tumor cells necessary to make a statistically robust diagnosis.
It would be desirable to provide a method and apparatus configured to rapidly acquire detailed cellular images from relatively large populations of cells, such that relatively small numbers of cancer cells present in a larger population can be statistically detected.